The present invention relates to a device and a method for safely recognizing switch positions of a rotary switch.
Manually operated rotary switches are used for different electrical applications, for example for entering parameters into electronic control circuits. The rotary switches are provided with a contact/sensor system and with a detent mechanism. The detent mechanism determines the number of possible switch positions and, if limit stops are provided, the angle between the left and right limit stops. The contact/sensor system is evaluated by a processing electronics connected to the switch, thereby determining the switch position. For example, on an electric stove, the switch position determines of the heating power of the associated heating plate.
Conventional devices use rotary switches with redundantly configured, galvanically separated contacts for selecting or switching functions associated with the safety of the device. The contacts are herein separately connected to a redundantly configured controller which, depending on the output encoding generated by the rotary switch, reads the switch position in Gray/Hex encoding or directly without encoding. Read errors, wiring defects and switch defects are recognized by comparing switch position values.
Such conventional rotary switches with redundantly configured contacts have several disadvantages. They are expensive, require a larger installation space, and require a potentially large number of redundant outputs depending on the number of switch positions, and a correspondingly large number of redundant controller inputs.
The German patent publication no. DE 100 09 707 A1 describes a safety switch with a first and second input switch, with the corresponding switch position of the first and second input switch redundantly defining an input-side control value.
The German patent publication no. DE 198 26 875 A1 describes a numerical control with a remote input device, wherein user input is redundantly preprocessed. The output signals of all input devices are herein transmitted to two processors, with the two processors determining from the user input data for a mutual plausibility check.
It would therefore be desirable to provide an improved device and method for determining safely, easily and cost-efficiently and with reduced wiring requirements of the switch positions of a rotary switch which provides output signals in the form of two sinusoidal, analog, switch position signal values that have a predetermined amplitude characteristics and are representative of the actual switch position angle.
According to one aspect of the present invention, a device for safely recognizing a switch position angle of a rotary switch includes two redundantly configured computer units that determine discrete switch positions of the rotary switch by evaluating two actual analog switch position signal values having a predetermined amplitude characteristic which reflects the switch position angle, with each computer unit separately checking the actual analog switch position signal values for plausibility. If the two digitized actual switch position signal values are provided to the first computer unit and the second computer unit in the form of sinusoidal signals having each a constant amplitudes and being phase-shifted with respect to each other by 90xc2x0, then the plausibility check is performed such that the signals are deemed to be plausible if the sum of the respective squares of the digitized actual switch position signal values supplied to the first computer unit or the sum of the respective squares of the digitized actual switch position signal values supplied to the second computer unit is located in a predefined range.
According to another aspect of the invention, a method for safely recognizing a switch position angle of a rotary switch includes the steps of evaluating with two redundantly configured computer units two actual analog switch position signal values having a predetermined amplitude characteristic which reflects the switch position angle, with each computer unit separately checking the actual analog switch position signal values for plausibility, determining discrete switch positions of the rotary switch from the evaluated two actual analog switch position signal values, providing the two digitized actual switch position signal values to the first computer unit and the second computer unit in the form of sinusoidal signals having each a constant amplitude and being phase-shifted with respect to each other by 90xc2x0, and performing a plausibility check such that the signals are deemed to be plausible if the sum of the respective squares of the digitized actual switch position signal values supplied to the first computer unit or the sum of the respective squares of the digitized actual switch position signal values supplied to the second computer unit is located in a predefined range.
The analog actual switch position signal values can be implemented in a particularly simple manner as sinusoidal signals; however, the signals can also have a triangular shape.
If the two actual switch position signal values are phase-shifted by 90xc2x0 relative to each other, then the switch positions and/or the switch position angles can be determined from the two actual switch position signal values.
The aforedescribed plausibility check is easy to perform and can advantageously be used to identify, for example, a wiring discontinuity of an actual switch signal value.
According to a first advantageous feature of the method of the invention, if the plausibility check indicates that the signals are not plausible, the digitized actual switch position signal values supplied to the first or second computer unit, or the switch positions determined therefrom are identified as being faulty, and suitable measures can be taken depending on the severity of the error.
It has been observed that when the plausibility check of the corresponding digitized switch position signal produces errors, the determined switch position can already be identified early on as being faulty, and suitable measures can be initiated depending on the severity of the error. One of such measure can be, for example, to switch off the associated computer unit.
According to another advantageous feature of the method of the invention, the two actual switch position signal values can be sinusoidal, and the switch positions can be calculated in the form of the switch position angles xcex1 separately in the first computer unit through the relationship
xcex1=arc tan [X1/Y1],
wherein X1 corresponds to the first digitized actual switch position signal value supplied to the first computer unit and Y1 corresponds to the second digitized actual switch position signal value supplied to the first computer unit, and in the second computer unit through the relationship
xcex1=arc tan [X2/Y2],
wherein X2 corresponds to the first digitized actual switch position signal value supplied to the second computer unit and Y2 corresponds to the second digitized actual switch position signal value supplied to the second computer unit, wherein in each of the computer units a phase of the first digitized actual switch position signal value lags a phase of the second digitized actual switch position signal value by 90xc2x0 and wherein the amplitudes of each of the digitized actual switch position signal values are constant.
A corresponding switch position angle xcex1 can be computed from the two actual switch position signal values in each computer unit by using a simple trigonometric function.
According to another advantageous feature of the invention, angular ranges that correspond to detent positions of the rotary switch position angles xcex1 can be identified and discrete switch position angles xcex1D can be associated with the angular ranges. In this way, discrete switch position angles xcex1D that correspond to the detent positions of the rotary switch can be easily determined from only two analog actual switch signal values.
According to another advantageous feature of the method of the invention, the computed switch position angles xcex1 or the discrete switch position angles xcex1D can be exchanged between the first and second computer units and crosswise compared with each other. In this way, each computer unit can separately identify faulty switch position angles xcex1 and/or faulty discrete switch position angles xcex1D.
According to yet another advantageous feature of the method of the invention, the effect on a subsequent process can be minimized by, for example, identifying the determined switch positions as being faulty if the crosswise comparison indicates an insufficient agreement between the calculated switch position angles xcex1 or between the discrete switch position angles xcex1D, with suitable measures then being taken depending on the severity of the error. The measures can include, for example, an optional warning or the entire subsequent process can be shut down if greater deviations are detected.
The device and method according to the invention can be used, in particular, for industrial controls where a switch position of a rotary switch which only includes the two aforedescribed analog outputs should be reliably identified. For example, the rotary switch can be installed in control panels for machine tools or production machines as a so-called override rotary switch to affect the spindle or rotation speed. The switch according to the invention can reliably identify switch position of the rotary switch, in particular when used to set limit values.